Process for forming dye images

ABSTRACT

A PROCESS FOR FORMING DYE IMAGES COMPRISING FORMING ELECTROSTATIC LATENT IMAGES ON A SHEET COMPRISING AN ELECTROPHOTOGRAPHIC SENSITIVE LAYER COMPOSED OF A FINELYDIVIDED ZINC OXIDE PHOTOCONDUCTIVE POWDER AND AN INSULATING RESIN ON A WATER-RESISTANT SUPPORT AND CONVERTING SAID LATENT IMAGES INTO GELATIN IMAGES BY DEVELOPING WITH AND ELECTROPHOTOGRAPHIC DEVELOPER CONTAINING A FINELYDIVIDED GELATIN POWDER, FIXING SAID GELATIN IMAGES AND HARDENING SAID GELATIN IMAGES ON SAID SHEET, REMOVING SAID PHOTOCONDUCTIVE ZINC OXIDE IN SAID ELECTROPHOTOGRAPHIC SENSITIVE LAYER ON SAID SHEET AND WASHING SAID ELECTROPHOTOGRAPHIC SENSITIVE LAYER ON SAID SHEET WITH WATER, SOAKING SAID SHEET IN AN ORGANIC SOLVENT WHICH DOES NOT DISSOLVE SAID WATER-RESISTANT SUPPORT AND SAID INSULATING RESIN, PLACING SAID SHEET WETTED BY SAID SOLVENT SO AS TO CLOSELY CONTACT THE SUPPORT SIDE WITH A METAL PLATE MAINTAINED AT A TEMPERATURE RANGING FROM A MAXIMUM OF 60*C. ABOVE TO A MINIMUM OF 20*C. BELOW THE BOILING POINT OF SAID SOLVENT, WHEREBY SAID ORGANIC SOLVENT IS EVAPORATED, CONTACTING SAID GELATIN IMAGES ON SAID SHEET WITH AN AQUEOUS DYE SOLUTION WHEREBY THE DYE IS ABSORBED INTO THE GELATIN IMAGES, REMOVING EXCESS DYE SOLUTION FROM SAID GELATIN IMAGES ON SAID SHEET BY WASHING SAID SHEET WITH AN ACID AQUEOUS SOLUTION, AND CONTACTING SAID GELATIN IMAGES WITH A DYE RECEPTIVE LAYER, WHEREBY SAID DYE IS TRANSFERRED FROM SAID GELATIN IMAGES TO SAID DYE RECEPTIVE LAYER, IS DISCLOSED.

Jan. 29, SADAO OSAWA ET AL PROCESS FOR FORMING DYE IMAGES Filed May 25, 1972 FIG. 4

United States Patent US. Cl. 96-1 R 24 Claims ABSTRACT OF THE DISCLOSURE A process for forming dye images comprising forming electrostatic latent images on a sheet comprising an electrophotographic sensitive layer composed of a finelydivided zinc oxide photoconductive powder and an insulating resin on a water-resistant support and converting said latent images into gelatin images by developing with an electrophotographic developer containing a finelydivided gelatin powder, fixing said gelatin images and hardening said gelatin images on said sheet, removing said photoconductive zinc oxide in said electrophotographic sensitive layer on said sheet and washing said electrophotographic sensitive layer on said sheet with water, soaking said sheet in an organic solvent which does not dissolve said water-resistant support and said insulating resin, placing said sheet wetted by said solvent so as to closely contact the support side with a metal plate maintained at a temperature ranging from a maximum of 60 C. above to a minimum of 20 C. below the boiling point of said solvent, whereby said organic solvent is evaporated, contacting said gelatin images on said sheet with an aqueous dye solution whereby the dye is absorbed into the gelatin images, removing excess dye solution from said gelatin images on said sheet by washing said sheet with an acid aqueous solution, and contacting said gelatin images with a dye receptive layer, whereby said dye is transferred from said gelatin images to said dye receptive layer, is disclosed.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention relates to a color printing process based on a recording process utilizing electrostatic latent images such as an electrophotographic process and an electrostatic recording process, and especially to an improvement in a dye transfer process which comprises developing electrostatic latent images to convert them into gelatin images and utilizing the resulting gelatin relief.

(2) Description of the prior art As methods for obtaining color prints having a good quality, two methods have been widely practiced at present. The first method, which is the most widely used, is of combining silver halide emulsions with color developing process. The second one is a dye transfer process which comprises carrying out tanning development using silver halide emulsions and utilizing the resulting gelatin relief, which generally prevails as the technicolor process.

In comparing these two methods, the former is suitable for a mass production. However, the images obtained are insufficient in durability and especially in light-resisting properties. On the contrary by the latter (the dye transfer process), images which have extremely high durability can be obtained. This dye transfer process closely approaches printing. Accordingly, a commercial profit is improved in a case of producing a large number of duplicates from one original. But it is not suitable for produc- 3,788,845 Patented Jan. 29, 1974 ICC ing a small number of duplicates, because the cost per a duplicate becomes particularly high.

This is because time and skill are required for obtaining the gelatin relief to be used as the original plate.

On the other hand, a method for obtaining the gelatin relief using an electrophotographic process is described in France Pat. No. 1,595,848.

Furthermore, a method is disclosed in Germany patent publication No. OLS 2,005,267, or British Pat. No. 1,257,- 296. Namely, a color printing process is known which comprises forming electrostatic latent images on an electrophotographic sensitive layer containing a photoconductive zinc oxide as the main photoconductor, changing the latent images into gelatin images using an electrophotographic developer containing a finely divided gelatin powder, and subjecting to the following treatments, that is, (A) removing the zinc oxide included in the electrophographic sensitive layer using an acid, (B) contacting the gelatin images with a dye solution containing a dye dissolved in a solvent mainly consisting of water to cause absorption of the dye into the gelatin images, (C) removing the excess dye solution on the gelatin images by washing with an acidic aqueous solution, and (D) contacting a layer which is capable of being readily dyed by the dye with the gelatin layer to transfer the dye to be caapble of being readily dyed layer. In this process, Step (A) is necessary to remove the zinc oxide which is the basic component which exhibits an obstructive function to the transfer of the acid dye. As the result of studies, it has been found that such a process has the following disadvantages.

Namely, in the gelatin image supporting sheet after removing the zinc oxide of Step (A), the binder resin layer forms a porous liquid storing layer. The gelatin images are relatively easy to break, because they are supported on the binder layer which forms the liquid storing porous layer. Further, since the dye solution is occluded in the spaces of the liquid storing layer in the next Step (B), it is impossible to remove the absorbed dye solution by washing in Step (C). Thus, it has been confirmed in the dye transfer treatment of the Step (D) that unevenness of the image portion and fog of the non-image portion are caused.

According to the present invention, the disadvantages of the above-described method has been improved. Namely, a first object of the present invention is to produoe color prints easily and cheaply using the dye transfer process. Namely, an object is to provide an improved dye transfer process in which a gelatin relief obtained by the electrophotographic process is utilized.

A second object is to provide a method for obtaining uniform distinct color images having a high image density but a low fog density using a dye transfer process in which the gelatin relief is obtained using the electrophotographic or electrostatic recording process.

A third object is to provide a process by which the printing durability is improved by reinforcing the gelatin relief.

SUMMARY OF THE INVENTION The present invention for forming dye images comprises the following treatments after forming electrostatic latent images on an electrophotographic sensitive layer composed mainly of photoconductive zinc oxide and an insulating resin on a water-resisting support and changing the latent images into gelatin images using an electrophotographic developer containing a finely-divided gelatin powder:

l) Removing the photoconductive zinc oxide included in the electrophotographic sensitive layer and washing with water;

(2) Soaking in an organic solvent which does not dissolve the water-resisting support and the insulating resin, placing the sheet which carries the gelatin images wetted by the solvent so as to contact closely the support side with a metal plate which can be maintained at a temperature of a maximum of 60 C. above and a minimum of 20 C. below the boiling point of the organic solvent, and evaporating the organic solvent;

(3) Contacting the gelatin images with a dye solution which contains a dye dissolved in an aqueous solvent to absorb the dye into the gelatin images;

(4) Removing the excess dye solution on the gelatin images by washing with an acid aqueous solution (namely, rendering the dye insoluble at once), and

(5) Contacting the gelatin images with a layer which is easily dyed by the dye to transfer the dye to the layer.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS FIG. 1 shows the state in which a photoconductive layer composed of a photoconductive substance 13 and an electrically insulating binder resin 14 applied on a support film 11 having a layer of a low electric resistivity 12 is developed with a gelatin toner 15.

FIG. 2 shows the state in which the photoconductive substance is removed by acid treatment of the photoconductive sheet. The gelatin toner thereon shows a state that fixed previously by steam and then hardened.

FIG. 3 shows the state after the organic solvent treatment and evaporation of the solvent elements of the present invention.

FIG. 4 is a sectional view of an example of an apparatus for evaporating the organic solvent.

DETAILED DESCRIPTION OF THE INVENTION The above-described color printing process of the present invention comprises, for example, the following steps:

(I) An electrophotographic sensitive layer containing zinc oxide is electrostatically charged in a dark place and is subjected to image-exposure to form electrostatic latent images;

(II) The sensitive layer carrying the electrostatic latent images is developed using an electroph-otographic developer containing a gelatin toner (for example, an electrophotographic liquid developer which contains a gelatin toner in a carrier liquid);

(III) The resulting gelatin images are fixed and hardened using any suitable method;

(IV) The sheet which has the resin layer of the electrophotographic sensitive layer and carries the gelatin images is washed with water;

(V) The sheet is soaked in an organic solvent such as methanol, ethanol, isopropanol, acetone and methylethylketone;

(VI) The sheet is placed on a warmed stainless steel plate so as to contact closely the support side of the sheet with the plate in order to evaporate the organic solvent;

(VII) The gelatin images are brought into contact with an aqueous solution of a water soluble dye to absorb the dye into the gelatin images;

(VIII) The excess of the solution of the dye on the gelatin relief is removed by washing with an acid washing solution;

(IX) A sheet to be dyed which has a readily dye absorbable surface layer is disposed so as to contact the layer to be dyed, with the gelatin images. At this point in the dye transfers to the layer to be dayed and final color images are obtained on the sheet to be dyed. By repeating Steps (VII), (VIII) and (IX) using the same gelatin relief, a large number of sheets having dye images can be obtained.

As was described above, the present invention involves washing with water after removing the photoconductor (for example, zinc oxide) using the acid and carrying out Steps (V) and (VI), that is, soaking the sheet having the binder resin layer which forms a liquid storing layer and carries the gelatin images thereon in the organic solvent, and contacting the sheet wetted 'by the solvent with a warmed metal plate having a flat surface so as to contact closely the support side of the sheet with the flat surface to evaporate rapidly the organic solvent. If the transportation of the color images is carried out excluding the use of the above-described Steps (IV), (V) and (VI) which are elements of the present invention, only images which have a comparatively heavy fog and unevenness are obtained. Furthermore, it has been found that printing durability of the gelatin relief is insufficient.

The fact that improvement of the printing durability and decrease of density of fog and unevenness are at tained by soaking in the organic solvent and drying by contacting with the heated metal plate by the present invention is believed as based on the following reason.

In producing a photoconductive sensitive paper from a photoconductive substance such as zinc oxide and an insulating resin as the binder, a powder of the photoconductive substance and the resin generally are mixed. The mixture is then applied to a support and dried. In this case, it is believed that all surfaces of the particles of the photoconductive substance are not completely covered with the binder resin but the particles themselves contact each other through the binder resin to form a photoconductive layer. Consequently, the photoconductive particles are eroded gradually at the surface thereof and dissolve in the step of treating with the acid. Examples of the acid are acetic acid and nitric acid. Thus the skeletonized binder resin layer remains together with the gelatin images and the support to form a liquid storing porous layer. However, when this sheet is soaked in the organic solvent, the binder can be considered as slightly swollen. Then the organic solvent is rapidly removed by evaporation by which the slightly swollen binder resin is considered to form a continuous uniform film by heat at this time and by the function of the solvent. Accordingly, the binder resin layer subjected to the organic solvent treatment changes into a uniform film which loses the liquid storing property, by which adhesion of the gelatin forming the images to the support is improved and the mechanical strength of the film increases. Thus, the images obtained have a very low fog density and a very little unevenness, that is, distinct uniform images are finally obtained.

The electrophotographic sensitive element used in the present invention is one prepared by providing a sensitive layer composed of zinc oxide as the main photoconductor and an insulating resin on a water-resisting support. Suit able insulating resins which can be used in the present invention include both thermo-setting resins and thermoplastic resins. The thermo-setting resins may be those obtained by appropriately curing an alkyd resin, an epoxyester resin, an acrylic resin, a silicone resin and the like. The curing can be effected using any of the conventional procedures. For example, an alkyd resin containing a drying oil, an epoxyester resin and a silicone resin can preferably be cured by using oxygen and a metallic soap as a catalyst. A typical procedure for curing the epoxyester resin is disclosed in US. Pat. No. 3,152,894. An alkyd resin, an epoxyester resin and an acrylic resin, each containing primary or secondary hydroxy groups, can preferably be cured with a polyisocyanate as disclosed in British patent specification No. 1,237,03 6. The curing of the alkyd resin and the epoxyester resin can also be effected with a melamine resin, benzoguanamine or the like in accordance with the teaching in German Pat. OLS 2,100,926. The thermo-plastic resins include vinyl chloride/vinyl acetate copolymer, vinyl acetate/ acrylic ester copolymer, acrylic resin, polystyrene, styrene/butadiene copolymer, vinyl acetate/crotonic acid copolymer and the like. When these resins are used, it is preferred that the Mvent f tlhe resins has a weak solubilizing property.

The photoconductive materials which can be used together with the zinc oxide include CdS, CdSe, Cd(S,Se), ZnS, TiO anthracene, polyvinylcarbazole, carbazole derivatives, as well as CdS.nCdSO which is disclosed in German patent publication No. OLS 2,028,121. Examples of inorganic photoconductive materials are enumerated in US. Pat. No. 3,121,006. Generally, the photoconductive materials may be those which do not adversely affect the dye transfer of the dyestuff for dye transfers even if they are not soluble in acids.

In the process of the present invention, it is preferred that the support have water-resisting properties and acid resisting properties, because the acid treatment is practiced in order to remove the zinc oxide. As the support, triacetyl cellulose films, polyethylene terephthalate films, and polycarbonate films are especially preferred. In general, a layer having a low electric resistivity is usually provided between the above described sensitive layer and the support. Therefore, it is suitable to choose a layer having the low electric resistivity 'which does corrode quickly due to the acid treatment.

The organic solvent used in the present invention should not dissolve gelatin, the Water resisting support or the binder resin. Further, it is preferred to have a boiling point of less than 150 C., because if the boiling point is too high, the sheet must be heated at a high temperature to remove the solvent. Where the binder resin is a thermosetting resin, the following organic solvents are preferably used. Namely, methanol, ethanol, isopropyl alcohol, methyl acetate, ethyl acetate, diethylketone, toluene, benzene, xylene and cyclohexane etc. are suitable for use. These solvents have a boiling point above 30 C. and less than 150 C. and an evaporation rate greater than 50, based on the evaporation rate of n-butyl acetate being 100, as shown by the following:

Evaporation Rate Evaporation time of n-butyl acetateX 100 Evaporation time of the test solvent (at 25 0.)

Where the binder resin is a thermo-plastic resin, the resin used should not dissolve in the organic solvent. In general, ester type solvents and ketone type solvents are not suitable for use.

As was described above, the organic solvents can be used alone or as mixtures of two or more thereof.

When a water-miscible solvent such as methanol, ethanol, acetone or the like is used, the sheet which has been subjected to acid treatment and Washing with water can be soaked in the water-miscible solvent, such as methanol, isopropyl alcohol, methyl acetate, ethyl acetate, diethylketone and the like, as illustrated above. When a waterimmiscible solvent such as cyclohexane, toluene, benzene, xylene, or the like is used, the sheet which has been subjected to the acid treatment and washing with water is first soaked in water-miscible organic solvent so as to replace the water contained in the wetted sheet with the above water-miscible organic solvent (acetone being preferable), and the thus treated sheet is then soaked in an organic solvent which is miscible with the above watermiscible organic solvent as enumerated above. The above replacement of water with the water-miscible organic solvent will not be necessary if the wetted sheet is dried directly after the washing with water. The solvent used for the soaking will be determined depending upon the type of the binder used for the photoconductive layer.

In the present invention, the support side of the sheet is brought into close contact with the heating plate in order to evaporate the organic solvent. As the heating plate, metal plates which are heat conductive such as those of stainless steel, copper, aluminum and iron plated or coated are preferably used. A heat source for heating such a metal plate is steam or electrothermic wire, and it is preferable to use those for which the temperature of the heating plate can be easily controlled. The temperature of the heating plate depends upon the types of organic solvents used,

and is preferable to range from a maximum of 60 C. above to a maximum of 20 C. below the boiling point of the solvent. It has been found that a more preferred range of the temperature is from a maximum of 50 C. above to a minimum of 10 C. below the boiling point of the solvent. Still further, it is preferred to use a solvent having a boiling point of from about 30 to C.

In any case, the organic solvent should be evaporated at a temperature below the heat-resisting temperature of the sheet film of the support. When the sheet is heated at a temperature above the heat-resisting temperature thereof, the sheet is easily distorted and the flatness thereof is injured. This causes an uneven transfer at the dye transfer step making it impossible to obtain uniform images. Further, when the evaporation of the organic solvent is not conducted rapidly when the heating temperature is too low, isolated uneven areas remain on drying and consequently ditficulty in dye transferring occurs too. As a result, the solvent should be evaporated uniformly, and rapidly.

In FIG. 1, a part of the photoconductive sensitive layer developed with a gelatin toner (see British Pat. No. 1,255,762) is shown. In FIG. 1, finely divided particles 13 of a photoconductive substance such as zinc oxide are applied to a support film 11 having a layer of a low electric resistivity 12 together with an insulating binder resin 14. A gelatin toner image 15 adheres to the surface of the sensitive layer. When the developed gelatin toner is fixer, hardened and treated with an acid, the photoconductive sensitive layer and the toner image are in the state shown in FIG. 2.

In FIG. 2, the greater part of the photoconductive particles is removed by acid treatment, for example, with acetic acid or nitric acid to form a porous layer 25 which easily stores the dye solution. A number of openings 27 exist in the layer. The gelatin toner 26 is supported by only the binder resin layer 23. Although the photoconductive particles 24 covered with the binder resin 23 exist in a very small amount, they are not a hindrance to the subsequent treatments. In such a state, adhesion of the binder resin 23 to the gelatin toner 26 and to the support film 21 having a layer of low elecLric resistivity 22 is not sutficient and is mechanically wea FIG. 3 shows the condition of the sensitive layer subjected to the organic solvent treatment and drying which are elements of the present invention. Namely, the binder resin layer 33 supported on the support film 31 becomes a homogeneous continuous layer and the openings 27 shown in FIG. 2 have disappeared. Further, adhesion of the binder layer 33 to the gelatin toner 35 and to the layer having a low electric resistivity 32 is improved and the mechanical strength thereof increases. 34 are photoconductive particles surrounded completely by the binder resin 33, which do not hinder the dye transfer.

FIG. 4 shows an example of an apparatus for drying after soaking in the organic solvent. Super heated steam is introduced into a heating box 41 made from metal plates through inlet 42 and outlet 43. On the way fins 45 are provided in order to improve conductivity and maintenance of the temperature. A support film 47 having a binder resin and carrying toner images which has been treated with the organic solvent is brought into close contact with the fiat outer surface 46 of the heating box 41, and dried by holding it in contact using stoppers 44 at the four corners.

As the dyes used for transferring in the present invention, acid dyes and mordant dyes are preferably used.

Examples of suitable dyes are as follows:

Cyan dyes: Color Index, Acid Blue 45 (CI. 63010), Acid Green 16 (Cl. 44025), Acid Green 1 (Cl. 10020), Acid Blue 1 (CI. 42045), Acid Blue 9 (CI. 42090) and Acid Blue 54 (no CI. number, anthraquinone dye).

7 Magenta dyes: (Color Index), Acid Red 80 (CI. 68215), Acid Red 34 (C.I. 17030), Acid Red 1 (CI.

18050), Acid Violet 19 (Cl. 42685) and Acid Violet 7 (CI. 18055).

Yellow dyes: (Color Index), Acid Yellow 23 (Cl. 19140), Acid Yellow 11 (Cl. 18820), Acid Yellow 34 (CI. 18890) and Direct Yellow 12 (Cl. 24895).

Suitable examples of dye receptive layers are disclosed in P. Glafkides, Photographic Chemistry, vol. 2, pp. 696- 699, Fountain Press, London, 1962, and suitable dye transfer processes are disclosed in US. Pat. Nos. 3,549,- 359; 3,563,733; 3,615,410; and 3,622,515.

The images obtained by the present invention have a high quality, an excellent light-resisting property and a good shade. Namely, deep colors are reproduced because there is no surface reflection in comparison with the images obtained electrophotographically using toners of each color. Further, faithful color reproduction is obtained, because each color of which multicolor images are composed is sufiiciently transparent and mixing of the colors can be carried out completely. Further, it is possible to make a number of prints by supplying the dye to the resulting images and transferring because the once obtained gelatin relief images can be used repeatedly many times.

The present invention is particularly effective where zinc oxide is used as the photoconductor in the electrophotographic sensitive layer. Further more, the invention is effective for the photoconductive layer where other photoconductors are used together with the zinc oxide. Photoconductors which can be used together with the zinc oxide include CdS, CdSe, Cd(S,Se), ZnS, ZnSe, TiO anthracene, polyvinylcarbazole and carbazole derivatives. These photoconductors can be removed using acids from the sensitive layer together with the zinc oxide, or they do not disturb the dye transfer step if they remain in the sensitive layer.

The present invention will be explained in greater detail by reference to the following examples.

EXAMPLE 1 5 g. of photographic use gelatin was added to 95 g. of distilled water. After 30 minutes, the gelatin was swollen. The mixture was then warmed at '60" C. to prepare a transparent aqueous gelatin solution.

To ml. of this aqueous gelatin solution, methanol was added while keeping it at 45 C. until the solution became cloudy. The amount of the methanol added totalled 11 ml. 0.5 ml. of distilled water was then added in order to remove cloudiness. Thus a solution of gelatin in a water-methanol solvent mixture was obtained. This solvent mixture solution was dispersed using ultrasonic waves in the following solution.

Acetone 980 Cotton seed oil Thus, a milk-white gelatin dispersion was obtained. To this dispersion, a solution having the following composition was added while stirring.

The resin component of this varnish was insoluble in acetone and soluble in a carrier liquid.

By addition of the solution, aggregation of the resin immediately in the liquid was observed. After minutes, almost all of the aggregate precipitated and then a supernatant fluid was removed by decantation. 800 ml. of acetone was then added to the precipitate with stirring. After being allowed to stand for 15 minutes, a supernatant fluid was removed by decantation, by which 200 ml. of a liquid which contained the precipitate was obtained. This liquid was subjected to centrifugal separation to obtain a resin precipitate which contained fine gelatin particles. All of this precipitate was added to the following solvent mixture with stirring.

Toluene 20 Xylene 35 Cotton seed oil 6 Cyclohexane 1600 Kerosene 400 Thus a light milk-white electrophotographic liquid developer was prepared.

Kerosene was added for the purposes of lowering the evaporation rate of the liquid developer. It was found that the gelatin toner in the liquid developer had a positive charge.

On the other hand, a homogeneous coating solution was prepared by adding 100 parts by weight of photoconductive zinc oxide and 20 parts (by weight, hereafter) of an epoxy ester of dehydrated castor oil fatty acid together with a hardener to a suitable amount of toluene. To this solution, a solution prepared by dissolving 20/ 1000 parts of Fluorescein and 20/1000 parts of Tetrabromophenol Blue in a small amount of ethyleneglycol monomethyl ether was added in order to expand the photosensitivity of the zinc oxide to the entire range of the visible spec trum. After adding a suitable amount of toluene, the solution was applied to an aluminium deposited polyethylene terephthalate film (thickness: 90,11.) so as to have approximately 8a of dry thickness. The product, when dried sufficiently in the dark place, functioned satisfactorily as the electrophotographic sensitive element.

This electrophotographic sensitive element was exposed to negative corona discharging in a dark place to charge uniformly the surface thereof. A color slide as the original was then loaded in an enlarger. The negatively charged sensitive element was exposed to light by projection after placing a red filter on the slide.

The exposed sensitive element was wetted with kerosene first and dipped quickly in the above-described liquid developer. In this case, the container was a stainless steel vat, which acted as a development electrode when the surface of the element which carried the latent images was brought close to the bottom of the vat. After soaking for approximately 90 seconds, the element was removed, washed with isoparafiin (Isoper E; trade name Ml. Glacial acetic acid 40 Distilled water 60 The sensitive element which carried the gelatin images was soaked in this solution. The solution was agitated often. After two minutes, the zinc oxide was removed from the surface of the sensitive layer and the entire surface possessed a metallic gloss due to the aluminium layer laid under the sensitive layer.

The sheet was then washed sufficiently with distilled water. After soaking the sheet in acetone for 2 minutes, the sheet was placed on the bottom of the stainless steel vat which was heated by exposing the back thereof to steam at 105 C. so that the support side of the sheet contacted the bottom closely. The acetone evaporated quickly, and consequently a gelatin relief having a metallic gloss which had no drying patches was obtained.

By the above-described treatments, a relief used for cyan printing was produced.

Similarly, another sheet was exposed using a combination of the same original and a green filter. Thus a relief used for magenta printing was produced using the same developing treatment. Similarly, a reliefused for yellow printing was produced using a blue filter.

The three matrices were soaked in aqueous solutions of Color Index. Acid Blue 54, Acid Violet 7 (CI. 18055) and Acid Yellow 23 (CI. 19140) for 2 minutes respectively. After removal, the sheets were washed with a washing solution containing acetic acid.

The excess of the dye solutions on the sheets were removed by this step. A phenomenon that the dyes absorbed into the gelatin images were not released in the washing solution was not observed.

On the other hand, a sheet to be dyed having a gelatin layer was soaked in an aluminum sulfate solution. After the above described mordanting the sheet was registered to and pressed against the above-described three gelatin reliefs one after another. Through this treatment, the dyes absorbed into each of the toner images were transferred onto the gelatin layer. Thus, a duplicate having extremely high quality was obtained. The fog density was 0.02. These reliefs were sufficiently durable that they could be used more than 200 times.

COMPARATIVE EXAMPLE Sheets washed only with water, that is, not treated with the organic solvent after the acid treatment in Example 1 were used as the relief. After soaking in the dye solutions, they were washed with an aqueous acetic acid solution and used for dye transferring. In the resulting images, the fog density was 0.28. Unevenness of the image was observed considerably.

EXAMPLE 2 The organic solvent treatment was carried out using methanol instead of the acetone used in Example 1, followed by drying. The resulting images were even and distinct, and had little fog.

EXAMPLE 3 The organic solvent treatment was carried out using ethanol instead of the acetone used in Example 1, followed by drying. The maximum reflection density of the resulting images was 1.72 and the fog density was 0.05.

EXAMPLE 4 The organic solvent treatment was carried out using a solvent mixture of methanol and isopropyl alcohol (2:1) followed by drying. The images obtained by the dye transfer treatment were distinct similar to those of Example 1.

While the invention has been described in detail and in terms of various embodiments thereof, it is apparent that various modifications and changes can be made therein without departing from the spirit and scope thereof.

What is claimed is:

1. A process for forming dye images comprising forming electrostatic latent images on a sheet comprising an electrophotographic sensitive layer composed of a finelydivided photoconductive powder containing at least zinc oxide and an insulating resin on a water-resistant support and converting said latent images into gelatin images by developing with an electrophotographic developer containing a finely-divided gelatin powder, fixing said gelatin images and hardening said gelatin images on said sheet, removing said photoconductive powder from said electrophotographic sensitive layer on said sheet and washing said electrophotographic sensitive layer on said sheet with water, soaking said sheet in a water-miscible organic solvent which does not dissolve gelatin, said water-resistant support and said insulating resin, evaporating said solvent rapidly and uniformly at a temperature below the heatresistant temperature of said support to form a continuous uniform film of said insulating resin, contacting said gelatin images on said sheet with an aqueous dye solution whereby the dye is absorbed into the gelatin images, removing excess dye solution from said gelatin images on said sheet by washing said sheet with an acid aqueous solution, and contacting said gelatin images with a dye receptive layer, whereby said dye is transferred from said gelatin images to said dye receptive layer.

2. The process for forming dye images of claim 1, wherein said finely divided photoconductive powder is acid soluble.

3. The process for forming dye images of claim 1 wherein said organic solvent has an evaporation rate of greater than 50 based on the evaporation rate of butyl acetate being 100.

4. The process for forming dye images of claim 5 wherein said solvent is selected from the group consisting of methanol, ethanol, acetone and methylethyl ketone.

5. The process for forming dye images of claim 1 wherein said support is selected from the group consisting of triacetyl cellulose film, polyethylene terephthalate film and polycarbonate film.

6. The process for forming dye images of claim 8 wherein the surface of said metal plate is plated or coated with an additional metal.

7. The process for forming dye images of claim 12 wherein the surface of said metal plate is plated or coated with an additional metal.

8. The process for forming dye images of claim 1 wherein said organic solvent has a boiling point ranging from 30 C. to C.

9. The process for forming dye images of claim 8 wherein said temperature of the metal plate ranges from 50 C. to 150 C.

10. The process for forming dye images of claim 1 wherein said rapid and uniform evaporating is carried out by placing said sheet wetted by said solvent so as to closely contact the support side with a metal plate maintained at a temperature ranging from a maximum of 60 C. above to a minimum of 20 C. below the boiling point of said solvent, whereby said solvent is evaporated.

11. The process for forming dye images of claim 10 wherein said metal plate has a flat surface.

12. The process for forming dye images of claim 10 wherein said metal plate has a fiat surface and is cylindrical.

13. The process for forming dye images of claim 1 wherein said insulating resin is a thermosetting resin.

14. The process for forming dye images of claim 13 wherein said organic solvent is a solvent containing at least one solvent selected from the group consisting of methanol, ethanol, propyl alcohol, acetone, methyl ethyl ketone. diethylketone, methyl acetate, and ethyl acetate.

15. The process for forming dye images of claim 1 wherein said insulating resin is a thermoplastic resin.

16. The process for forming dye images of claim 1 wherein said finely-divided photoconductive powder contains, in addition to Zinc oxide, at least one member selected from the group consisting of CdS, CdSe, Cd(S, Se), Zn S, TiO anthracene, and polyvinylcarbazole.

17. The process for forming dye images of claim 13 wherein said organic solvent contains at least one member selected from the group consisting of methanol, ethanol and propyl alcohol.

18. A process for forming dye images comprising forming electrostatic latent images on a sheet comprising an electrophotographic sensitive layer composed of a finelydivided photoconductive powder containing at least zinc oxide and an insulating resin on a water-resistant support and converting said latent images into gelatin images by developing with an electrophotographic developer containing a finely-divided gelatin powder, fixing said gelatin images and hardening said gelatin images on said sheet, removing said photoconductive powder from said electrophotographic sensitive layer on said sheet and washing said electrophotographic sensitive layer on said sheet with water, removing said water, soaking said sheet in a water immiscible organic solvent which does not dissolve gelatin, said water-resistant support and said insulating resin, evaporating said solvent rapidly and uniformly at a temperature below the heat-resistant temperature of said support to form a continuous uniform film of said insulating resin, contacting said gelatin images on said sheet with an aqueous dye solution whereby the dye is absorbed into the gelatin images, removing excess dye solution from said gelatin images on said sheet by washing said sheet with an acid aqueous solution, and contacting said gelatin images with a dye receptive layer, whereby said dye is transferred from said gelatin images to said dye receptive layer.

19. The process for forming dye images of claim 17 wherein removing said water is accomplished by drying said sheet.

20. The process for forming dye images of claim 15 wherein removing said water is accomplished by soaking said sheet in a water-misible solvent which is miscible with said water-immiscible solvent.

21. The process for forming dye images of claim 17 wherein said water-immiscible solvent is a member selected from the group consisting of cyclohexane, benzene, toluene and xylene.

22. The process for forming dye images of claim 17 wherein said rapid and uniform evaporating is carried out by placing said sheet wetted by said solvent so as to closely contact the support side with a metal plate maintained at a temperature ranging from a maximum of C. above to a minimum of 20 C. below the boiling point of said solvent, whereby said solvent is evaporated.

23. The process for forming dye images of claim 1 wherein said water-miscible organic solvent is capable of swelling said insulating resin.

24. The process for forming dye images of claim 17 wherein said water-miscible organic solvent is capable of swelling said insulating resin.

References Cited UNITED STATES PATENTS 3,654,865 4/1972 Tamai 961.8 X 3,677,766 7/1972 Tamai et al. 96-1 LY 3,549,359 12/1970 Hokjo et al 101-464 X 3,681,065 8/1972 Sato et al 101464 X 3,692,523 9/1972 Tamai et a1 961 LYX 3,001,972 9/1961 Kurz 96-1 RX 2,297,691 10/1942 Carlson 96-1 R ROLAND, E. MARTIN, JR., Primary Examiner U.S. Cl. X.R.

96--150, 1 LY, 1.2, 1.5, 1.8; 117-356, 37 LE; 151- 464, 470, 471 

